What is the purpose of hunching your back while you pass?

I don't think you're supposed to... You're supposed to have a straight back.

Good passers do not hunch their backs. What they are really doing is keeping low with their knees bent. Their weight is forward, on their toes, so that they can move to the ball quickly and easily. The looseness allows for quick movement, as you can't pass if you are tense. Hunching your back when you pass will actually lead to worse posture, and increase lower-back pain.

It's not that they're hunching their backs, it's that they're shrugging their shoulders as they pass. In order to get a really nice arched pass, you can't swing your arms. Instead, to get that same amount of power in a more controlled bump, you lift from the knees and shrug your shoulders, keeping your arms pointed towards the floor at about a 40-45º angle. I think that's what you're seeing, because hunching your back would not be beneficial that I can think of.

Hope this helps.

You should not have a hunched back. you should be bending at the knees and waist only. however having hunched shoulders means you are loser which will mean better passes. also this helps you stay low and move your arms for last second adjustments

you really shouldn't be hunched over but you round your shoulders forward so that your arms are out in front of you with a flat solid platform. hunching makes you stay low, in front of the ball, and puts your body in a better position to pass the ball to the correct person [setter] if you stand up with ur shoulders back . and you pass the ball it will most likely go straight up.. or even sometimes backwards over your head.. it really does make a difference.